This invention relates generally to air or fluid flow regulators, commonly known as "demand-type flow regulators" which operate or allow passage of air in response to a respiration demand signal fo a user employing the flow regulator in conjuncton with breathing equipment. More specifically, the present invention provides a means whereby the user's respiration demand signal will be substantially the same for either initially allowing the passage of inlet air or to maintain a continued flow of inlet air.
As stated, regulators for passing breathable air in response to a demand signal are commonly known as "demand-type flow regulators". Such regulators find particular use in surface and underwater breathing equipment such as utilized in firefighting, intensive care breathing apparatus for hospital use, and sports applications such as diving equipment. Such fluid or flow regulators are generally located in the air supply line from a tank of compressed air to the mouthpiece or face mask of the breathing equipment. Basically, demand-type regulators include a control valve which is normally closed to block ar flow. By inhaling through the mouthpiece, or through a corresponding port in the face mask, the control valve is momentarily opened to pass a quantity of air from the supply ank into the lungs of the user or operator. Unfortunately, the foregoing operation does not always occur with maximum efficiency. In practice, it is often difficult to open the control valve and to draw a sufficient quantity of air through the regulator. This initial effort required by the user to open a control valve is referred to as "the cracking pressure" in the unit. However, as the control valve of a flow regulator is opened, it has been found that the air flow therethrough develops venturi effects on the assembly employed to open such control valve which venturi effects tend to reduce the effort needed by the user to maintain the control valve in an open disposition. It is to be understood that this variance in effort required of the user exists at various levels of air pressure in the supply tank and even in the presence of a pressure reduction means which might be disposed between the supply tank and the inlet to the flow regulator whereby a substantially constant supply pressure of air is provided to the flow regulator inlet.
For a scuba diver using underwater breathing apparatus employing a regulator of such unbalanced design wherein he must exert relatively greater effort to initiate air supply than to maintain an air supply, a serious safety problem is presented and is particularly accentuated at appreciable water depths where physical exhaustion can be a rapid process. At such depths, the diver requires increased volumes of air. His suction effort naturally increases in an attempt to increase the flow of air through a regulator. This increased effort, in view of the "cracking resistance" found in prior art devices accelerates his exhaustion and causes a demand for even greater volumes of air. At this point even stopping to rest while still under pressure will not ease the demand for great volumes of air and the diver begins to gasp for breath. To prevent drowning, the diver must then either return to shallower water where smaller volumes of air are required for normal breathing or to the surface. In such situations, it will be obvious to those familiar with underwater diving that a safety hazard is presented should a diver return to shallower water in too rapid a manner.
The prior art includes various types of demand-air regulators for breathing equipment. Generally such structures include a flexible, respiration-responsive diaphragm which abuts a pivoted lever arm which in turn is coupled to an air inlet valve in the air regulator structure. Upon inhalation of the user, the diaphragm is flexed so as to pivot the aforesaid lever arm which in turn opens the air inlet valve. However, the pivoted arms in the prior art include substantially fixed pivot points so that the mechanical advantage employed to open the inlet valve is the same during initial opening of the valve and at later stages of valve opening. Such a constant mechanical advantage therefore reflects a relatively high effort on the part of the user to overcome the initial "resistance".